Log in

Auth with social network:

We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you!

Buttons:

Presentation is loading. Please wait.

1 Genetic regulation Genotype is not phenotype: bacteria possess many genes that they are not using at any particular time. Transcription and translation.

Published byModified over 5 years ago

Similar presentations

Presentation on theme: "1 Genetic regulation Genotype is not phenotype: bacteria possess many genes that they are not using at any particular time. Transcription and translation."— Presentation transcript:

1
1 Genetic regulation Genotype is not phenotype: bacteria possess many genes that they are not using at any particular time. Transcription and translation are expensive; why spend ATP to make an enzyme you don’t need? Operon –Genes physically adjacent regulated together Regulon –Genes dispersed but controlled by same proteins –Operator sequences must be same/similar

2
2 More on Regulation Two important patterns of regulation: Induction and repression. –In induction, the genes are off until they are needed. –In repression, the genes normally in use are shut off when no longer needed. Negative control –Binding of protein to the DNA prevents transcription Positive control –Binding of protein to DNA promotes transcription

3
3 Repressible operons Operon codes for enzymes that make a needed amino acid (for example); genes are “on”. –Repressor protein is NOT attached to DNA –Transcription of genes for enzymes needed to make amino acid is occurring. The change: amino acid is now available in the culture medium. Enzymes normally needed for making it are no longer needed. –Amino acid, now abundant in cell, binds to repressor protein which changes shape, causing it to BIND to operator region of DNA. Transcription is stopped. This is also Negative regulation (protein + DNA = off).

5
5 Regulation can be fine tuned The more of the amino acid present in the cell, the more repressor-amino acid complex is formed; the more likely that transcription will be prevented.

6
6 Structure of the Lac operon KEY: P O are the promoter and operator regions. lac Z is the gene for beta-galactosidase. lac Y is the gene for the permease. lac A is the gene for a transacetylase. lac I, on a different part of the DNA, codes for the lac repressor, the protein which can bind to the operator.

8
8 How the lac operon works When lactose is NOT present, the cell does not need the enzymes. The lac repressor, a protein coded for by the lac I gene, binds to the DNA at the operator, preventing transcription. When lactose is present, and the enzymes for using it are needed, lactose binds to the repressor protein, causing it to change shape and come off the operator, allowing RNA polymerase to find the promoter and transcribe. http://www.med.sc.edu:85/mayer/genreg1.jpg

9
9 Lactose is not actually the inducer Low basal levels of beta- galactosidase exist in the cell. This converts some lactose to the related allolactose which binds to the lac repressor protein. Synthetic inducers such as IPTG with a similar structure can take the place of lactose/allolactose for research purposes. http://www.search.com/reference/Lac_operon